Preheat the oven to 350F. Grease or brush non-stick mini-muffin tin with oil or melted butter.

Cut the sweet potato into small cubes and boil, steam or microwave until tender. Drain well and set aside.

Heat the oil and butter in a frying pan and cook the leek for 10 minutes, stirring occasionally, or until very soft and lightly golden. Add the garlic and cook for a further 1 minute. Cool, then stir in the feta, dash of nutmeg and sweet potato. Divide among the muffin holes (3/4 full).

Whisk eggs and cream together and season with salt, cracked black pepper, and a dash of nutmeg. Pour the egg mixture into each hole until three-quarters filled, then press the vegetables down gently.

Bake for about 20 minutes, or until golden and set. Leave in the tins for 5 minutes to cool, then ease out with a knife. Serve either hot or at room temperature.